I. Field of the Invention
This invention relates in general to processes for forming high molecular weight hindered phenols and intermediates therefor. This invention relates in particular to an improved catalyst/solvent system for the formation of hindered phenols.
II. Description of the Prior Art
The hindered phenols ultimately formed by the process of this invention and earlier processes have been widely used as antioxidants in food, packaging materials, stock chemicals, plastics and the like. A process to produce such hindered phenols is set forth in Rocklin et al., U.S. Pat. No. 3,026,264 which is incorporated herein by reference in its entirety. An improvement on the Rocklin et al. process is disclosed in my U.S. Pat. No. 4,340,767 which is also incorporated herein by reference in its entirety.
There exists a need to reduce the processing and materials cost used in the production of antioxidants such as 1,3,5-trimethly-2,4,6-tris(3,5,-di-tert-butyl-4-hydroxybenzl)benzene. The prior art processes have used, for example, 3,5-dialkyl-4-hydroxybenzly alcohol (also called 2,6-dialkyl-.alpha.-hydroxy-p-cresol) as an intermediate to produce the high molecular weight hindered phenols. The alcohol intermediates must be isolated from their reaction mass as a solid by means of centrifugation which is quite expensive. Also, adequate washing of the solid filter cake has proven difficult and some of the wash solvents may be carried forward into the product causing various problems.
The 3,5-di-tert-butyl-4-hydroxybenzyl alcohol is often used as an intermediate. However, this intermediate is insoluble in preferred solvents such as methylene chloride. Thus strict stoichiometry controls are required and undesirable side reactions with sulfuric acid catalyst may occur. Finally, the use of an alcohol intermediate produces significant amounts of "heel" and certain bisphenols which, while usable, tie the subject process to other processes and markets.
The substitution of alkyl ethers of intermediate alcohols has been suggested to produce high molecular weight hindered phenols. However, the ethers are not always available and their production has not been cost effective.